(1) Field of the Invention
This invention relates to controls for processing systems, and more particularly to controlling feeders according to the load on the processing equipment.
(2) Description of the Prior Art
Before my invention, load (power requirement) fluctuations caused problems in processing systems. Non-uniform characteristics of material being processed often resulted in wide variations in the load on the processing machines. The resultant load fluctuations often caused excessive wear of equipment, uneconomical operation and non-uniform product for the processing. Therefore, some means was necessary to control the load on the processing machines.
Workers in the art have previously controlled the load on processing machines by controlling the feed rate. Prior devices provided for variation in the feed rate only when the power to, or load on, the processing machine fell outside an upper or lower limit. The feed rate was altered until the power, or load, fell within the set limits.
DORAN, U.S. Pat. No. 2,129,049, is representative of such prior devices. In DORAN, when the power is outside the range, the rate of feed is constantly altered until the power input falls within the desired range. The power input is confined within a single given range, but may fluctuate within that range.
In DORAN, the feed rate is not preset for a given process load condition. The moment the process load returns to the max-min range, the feed rate is fixed at whatever level it adjusted to during a "lag time". In DORAN's process the lag time is the time interval between the moment at which the process load went outside the limits and the moment at which it returned within the limits. Therefore, in DORAN, the feed rate when the process load is within the limits is dependent upon the duration of the previous lag time.
This causes, among others, three problems. First, variance within the maximum and minimum limits is not regulated. Second, the constant alteration of the rheostat during the lag time will result, in most cases, in a non-optimum feed rate for a particular process load. Third, "zero" and "excessive" load rates are not accounted for. If the feeder runs out of material to be processed, there will be a "zero" load condition on the processing machine. Use of the prior devices would result in a constant increase in the feed rate until the feeder ran at top speed. Correspondingly, for a condition wherein the processing machine becomes choked with material and stops, the load rate will be extremely high, thereby constantly decreasing the feed rate to a zero level. However, the zero level will not be reached until after the period of time it takes the motor to wind the rheostat to the zero point.
I was aware of the following prior art before filing this application:
______________________________________ Sachs 682,642 Wyckoff 1,859,814 Meyer 1,963,371 Safar 3,305,720 Favre 3,732,472 Weigele et al 3,819,991 ______________________________________